Servo control systems use feedback to command a control actuator to reduce error between desired behavior and observed behavior of components of a system, as measured by a control sensor. A common example of this is a motorized, gimbaled telescope that may be given specific coordinates to observe a target. A servo control system acts to command motors in each axis of the telescope to minimize an error between known coordinates of the target and a current position of the telescope as determined by an angular position sensor. A “closed loop” controlled telescope would reject being pushed away from a commanded target position by external disturbances.
The real world limitation in this example, and other feedback control applications, is a speed that the desired position can be achieved and a closely related maximum frequency disturbance that the telescope system can reject. This limitation can be made more severe by time delays that introduce latency in a control loop of the servo control system. Every real world application has latency as a limitation (e.g., movement of components lags behind commands), and all digital control systems further introduce latency that is directly related to a sample rate of the digital system. Signal conditioning to reduce sensor noise further introduces additional latency.
A common physical manifestation of a feedback servo control system that is pushed to a relatively high bandwidth in the presence of latency is a potential for oscillation that occurs at or near a bandwidth frequency of the servo control system. Decreasing latency may require redesign of the servo control system or may not be possible. It might also require redesign of components of the underlying structural system, which can be costly.
What is needed is a method to increase control bandwidth of a servo control system in the presence of latency.